THE STRUCTURE AND DEFORMATION OF THE MURCHISON BASIN, SOUTH-ISLAND, NEW-ZEALAND

The Murchison Basin lies close to the Alpine Fault and has an evolutio n that is intimately related to the development of the New Zealand pla te boundary during the Tertiary. Faults in the Murchison Basin follow a regional NNE structural grain which is inherited from Paleozoic sutu res that were zones of weakness prior to the late Eocene inception of the basin. The Tainui Fault may be the southern extension of the Paleo zoic Anatoki Thrust that was reactivated during late Cenozoic compress ion. The Matiri and Maunga Faults, which mark the western margin to th e basin and the junction with a structurally high Karamea Batholith, a re late Eocene normal faults that have similarly been reactivated and overturned. The eastern boundary is formed by the Tutaki Fault, a sout heast-dipping thrust fault which delineates the Rotoroa Complex baseme nt block. Folds within the basin reach a depth of 8 km, whereas, on th e basin margins, they have formed as gentle drape folds over a warped basement surface. The dominant structural control for the Murchison Ba sin is WNW-oriented compression and reactivation of basement block-fau lts, rather than dextral or sinistral transpression associated with Al pine Fault movement. This has resulted in the basin being the deepest and most intensely deformed of the West Coast region.